Ready-made reading glasses are made and sold in assorted magnifications to allow wearers to choose the proper magnification for their requirements. The magnification is a measure of the diopter or focusing power of the lenses contained within each pair of eyeglasses. All diopter lenses have undesirable aberrations and prismatic effects which are encountered if viewed through any point away from the lens optical center. Viewing through significant aberrations and prism may cause eye fatigue, eyestrain, blurred vision, headaches, loss of concentration and difficulty reading or doing prolonged “near work” with eyeglasses. For that reason, guidelines have been set forth by the International Organization for Standardization (ISO) that call for horizontal prism tolerances of 0.66Δs (cm/m, abbreviated as: Δ) per pair, or less to ensure comfortable vision. One particular standard of interest is ISO 16034: “Ophthalmic optics—Specifications for single-vision ready-to-wear near-vision spectacles”. This standard provides the prism threshold for optimized vision by comparing any OCD setting a manufacturer may specify to the OCD of the finished reading glasses. While this standard as a quality control guideline is laudable, it has a serious flaw: failing to take into account that the OCD chosen by a manufacturer may be flawed, as it is potentially a mismatch for the over the counter consumer purchasing the product.
Aberrations and prism increase as a result of two constraints: 1) the diopter power (higher power lenses contain more aberrations and prism), and 2) the position of the line of vision relative to the optical center of the lens (looking through the inner or outer edge of the lens induces more aberrations and prism than looking through the optical center). If the wearer is looking through the optical centers of the lenses, then the aberrations and prism are minimized. However, if the wearer's eyes are spaced farther or closer than the specified OCD, excessive prism will occur. Thus, a manufacturer may specify an OCD setting that is too narrow or too wide for the majority of people, yet still pass this quality control standard. The ISO standard only requires that the eyeglasses are made according to the manufacturer's specification. Prior art and the ISO standard fail to recognize that the key to limiting prism to 0.66Δ or less while the glasses are being worn lies in proper OCD specification to accommodate the majority of wearers. Until the present disclosure, OCD settings have never been optimized to limit excessive prism from occurring for the range of wide to narrow eye spacings that are typical in the population.
Custom made prescription eyewear addresses the prism problem as each pair is made to ensure that unwanted aberrations and prism are minimized at the lens optical center. This is accomplished by the optical provider first measuring the user's separation between left and right eye, or pupillary distance (PD). FIG. 1. illustrates the pupils 1a and 1b and the PD 2a. Once the PD is known, then the prescription eyeglasses are custom made to match the separation between the optical centers to the user's PD.
Each lens, 3a and 3b as illustrated in FIG. 2, is mounted into an eyeglass frame held by lens mountings 6a and 6b. The lens 3a and 3b placement within the lens mounting 6a and 6b determines where the lens optical centers 4a and 4b are positioned. Ideally, the optical centers 4a and 4b will coincide with each of the user's pupils. In prescription eyeglasses, the optical provider is careful to mount the lenses 3a and 3b so that the optical centers 4a and 4b are positioned directly in front of the user's pupils. Hence, the OCD 5a matches the PD, resulting in minimal aberrations and prism as the wearer gazes straight ahead, as shown in FIG. 3.
However, in ready-made reading glasses, as seen in FIG. 4, the pupils 4a and 4b may be spaced such that the PD 2b may be wider than the pre-set OCD 5a between optical centers 4a and 4b. Or, as seen in FIG. 5, the pupils 4a and 4b may be spaced such that the PD 2c may be narrower than the pre-set OCD 5a between optical centers 4a and 4b. Discrepancies between PD and OCD create unwanted prism and aberrations.
In contrast to custom made prescription eyewear, OTC, ready-made eyeglasses, have a pre-set OCD such that only one OCD is offered by sellers. As the PD is known to vary greatly in the general population, and ranges from 45 millimeters (mm) to 80 mm, a single OCD cannot cover the range of normally occurring PDs.
The manufacturer selected, pre-set OCD setting has typically been one size to fit all, and the particular setting chosen by various suppliers varies widely with no stated rationale for selection of their particular OCD setting. Presumably, purveyors of readymade reading glasses believe the OCD setting that they specify is in agreement with the “average” PD of the population they intend to serve. Until the present invention, there was no agreement about the average, nor proper setting to choose, nor an identified way to scientifically calculate the best solution. Thus, the prior art shows a wide disparity in the OCD settings among the reading glasses offered by the various suppliers. And, the OCD setting(s) chosen for readymade reading glasses have not been ideal for optimizing vision for the greatest number of people. A study (see Refraction and Interpupillary Distance Measurements, Acta Opthalmol, 65:44-47) of 555 subjects found that available OTC readymade reading glasses were unsuitable for nearly 14.2% of the population. Further evidence that there is no agreed nor accepted value for best OCD setting(s), lies in an independent optical testing laboratory report (see Test Results and Report Colts Laboratory O-EMA 111507) which widely sampled more than 450 reading glasses from 8 different vendors and discovered a different mean OCD setting for each vendor, ranging widely, from 54 to 64 mm.
Thus, OTC, ready-made eyeglasses comprise excessive aberrations and prism for some wearers of eyeglasses. Aberrations and prism are more pronounced if the user requires higher powered eyeglasses or has a PD significantly wider or narrower than the offered pre-set OCD. Thus, some wearers are exposed to more aberrations and prism and may experience eyestrain or other symptoms such as impaired task performance, lower reading comprehension, headaches, and even neck and back pains.
Hence, given the wide variation in eye spacings, no single OCD setting is capable of minimizing aberrations and prism for all PDs. Yet, it is impossible to offer OTC readymade reading glasses to exactly match each and every PD setting, as the cost, inventory and space required would be prohibitive. Recognizing the fact that OTC readymade reading glasses with preset OCDs create prism and aberration, the New York State Optometric Council strongly opposed the over-the-counter sale and use of readymade reading glasses citing the failure to have lenses optically centered with the PD (see Sep. 2, 1988 memorandum in opposition to NY State Reading Glass law enactment). Similarly, the New York State Society of Opticians raised concern that with discrepancies between PD and OCD, readymade reading glasses result in unwanted prismatic effects causing double vision, eyestrain and headaches (see Aug. 25, 1988 letter opposing NY State Reading Glass law enactment). Yet, despite these protestations, the economic benefits of readymade reading glasses (less expensive and more readily available than custom made prescription eyeglasses) have outweighed the optical handicaps.
U.S. Pat. No. 4,762,406 reveals sliding moveable lenses in reading glasses as a means to position the OCD to accommodate the breadth of variations in PDs that occur in reading glasses users. This is a simple and elegant means of properly aligning the visual axes of the wearer with the optical centers of the lenses, thus limiting or eliminating undesirable prism and its problematic side effects. However, the sliding feature is subject to user error and repeated misalignment. Thus, the user of the glasses described in '406 are subject to periodic and multiple readjustments, and if not aligned properly, these reading glasses can cause more harm than good by creating excessive prism, the opposite effect of their intended use. Thus, there remains a great need for discovery of the best fixed OCD setting(s) that will minimize prism effects for the greatest number of wearers.
U.S. Pat. Nos. 7,357,505, 6,910,769 and 4,898,459 describe how to measure the PD of the wearer utilizing various devices and means. However, until the present invention, discovering a given user's PD for OTC reading glasses was an exercise in futility, as the optimum OCD settings for OTC reading glasses has never been identified. Until the present disclosure, there was no knowledge among manufacturers and vendors of readymade reading glasses as to a method for determining the best OCD or OCDs that will be suitable for the greatest number of people and maximizing their vision and comfort while maintaining a limited and practical number of offerings thus limiting costs, inventory and space requirements. The method for calculating the best OCD specifications is the solution to minimizing the troublesome prism that occurs from a mismatch of PD and OCD.
U.S. Pat. Nos. 6,910,769 and 4,898,459 both disclose reading spectacles comprising a film overlay. The overlay enables a person to identify a pair of spectacles having the correct optical center (i.e., OCD) to match the wearer's pupillary separation (i.e., the PD). The '769 patent discloses a combination of a pair of spectacles having two near focal powers and a type of display mechanism that allows the purchaser to choose not only the correct power needed, but also the correct pair of glasses to match the user's PD. Optical centers of finished reading glasses are marked at the place of manufacture, then a display device including an opaque polyvinyl static cling film having two holes therein is placed onto the lenses, at the place of manufacture, such that the holes in the film overlie the optical centers. When the user dons the glasses, if a solid round area is viewed, the spectacles have the correct size for the user's PD. If a figure eight or two holes is viewed, the PD is too wide. If the user views the outside edges, the PD is too narrow. By visual observation, the user can find the correctly sized reading glasses. Similarly, the spectacles disclosed in the '459 patent comprise an opaque film that allows the user to test suitability of the spectacles for their PD.
The eyeglasses comprising the film described in the '769 and '459 patents are made using a process that is expensive and interferes with vision while the user tries on the eyeglasses and attempts to look through the film. Therefore, there is a need for OTC ready made eyeglasses that do not comprise such a film and that can accommodate a variety of PDs, for single vision, bifocal and multifocal reading glasses, thus minimizing the aberrations and prism thereby increasing the comfort and wearability of the eyeglasses. Moreover, there is a greater need for a method and the results derived there from for determining which of the many possible OCD setting(s) are most capable of limiting prism for the majority of OTC readymade reading glass users. The present invention provides a method for determining the best OCDs to optimize vision in readymade reading glasses, and also provides for the practical application of the results and outcomes derived from implementation of this method.